Cored passageway formation



July 11, 1961 R. F. DALTON CORED PASSAGEWAY FORMATION 3 Sheets-Sheet 1Filed Jan. 13. 1956 R. F. DALTON CORED PASSAGEWAY FORMATION July 11,1961 3 Sheets-Sheet 2 Filed Jan. 15. 1956 INVENTOR. fiberzfflaforz,

July 11, 1961 R. F. DALTON CORED PASSAGEWAY FORMATION 5 Sheets-Sheet 3Filed Jan. 13. 1956 PERCENT HKOHOFLUOR/C #670 M/ M/XTl/HE United StatesPatent 2,991,520 CORED PASSAGEWAY FORMATION Robert F. Dalton, Chicago,Ill., assiguor to Howard Foundry Company, Chicago, 111., a corporationof Illinois Filed Jan. '13, 19 56, Ser. No. 558,987 12 Claims. (Cl.22-131) The present invention relates generally to the formation ofcored passageways in metal castings, and is directed particularly toovercoming the difliculties normally present in the formation of smallbore passageways having one or more curves. An important innovation ofthe invention is the provision and use of a flexible gas-permeablerefractory sleeve as the primary member of a core element.

Generally, there are two known methods of producing bores or passagewaysin castings. One of these methods involves machine operations, such asdrilling, after a casting has been made. The operation of drilling holesor passageways is inherently limited. The drilled passageways mustalways be straight or composed of two or more straight sections. Thismethod of forming passageways is not only an extra operation, thusinvolving extra expense, but involves the risk of spoiling a certainpercentage of castings due to the drifting of the drill to an extentthat the passageways do not run true. Even if drilled passageways meetbut are not precisely connected, turbulent flow may result because ofthe imperfect junction. This may result in an insufficient flow of fluidor foaming of the liquid with its attendant disadvantages.

The other common method of forming passageways in castings is to castthem to shape with suitable cores of refractory material as a part ofthe mold in which the metal is cast. Examples of castings formed in thismanner in the foundry industry are water cooled motor blocks and watercooled cylinder heads used in the automotive industry. Here the coredpassageways are formed by casting the metal around a core composed of arefractory aggregate such as foundry sand bonded with an organic bindersuch as core oil or resin. As a result of the casting operation the coredisintegrates and collapses and the refractory aggregate may be shakenout from the rough casting.

This latter method involves certain disadvantages and practicallimitations. The cores must be capable of venting the core gas generatedduring the metal pouring operation so that the gas may escape from themold without requiring its passage through the metal itself. Theformation of gas pockets within the casting results in the manufactureof an inferior casting which, in many cases, is completely non-useable.In the instance where a refractory aggregate such as sand is used, thecore gas escapes through the interstices of the aggregate in a desirablemanner.

An additional disadvantage accompanying the use of refractory aggregatecores is the practical limit experienced in the forming of passagewaysof small diameter. As the cores become smaller in diameter they becomemore fragile to manual handling and metal pouring, and since the crosssectional area of the core becomes smaller, the problem of venting thecore gas becomes greater. Therefore, this method is impractical in theforming of small diameters such as A inch to 5 inch or less due to thelack of a suitable material from which the core may be made.

Efforts have been made to devise other methods of forming coredpassageways, one being the use of cast-in stainless steel tubes. Thestubes must be accurately preformed to the desired longitudinal shape anddimensions,

accurately placed and supported in the mold, and molten amount of skillto produce.

metal cast directly around the tubes. The tube assemblies where severalpassageways are involved are expensive to manufacture as they require aconsiderable They have the further disadvantage of often havingimperfect interiors due to imperfect joints, weld spatter and flowingweld material. Thus it is necessary to test these tubes for pressuredrop before placing them in the mold to be sure that the in terior issufliciently clear for its intended use. It furthermore is necessary toexamine the exterior of the tube thoroughly to make sure that thesurface is clean and free of any foreign materials which will form gaspockets or otherwise prevent the molten metal from accuratelysurrounding the tubing. Still further, the cast-in metallic tube of thetype described increases the weight of the casting which is often a realobjection, particularly in the aircraft industry.

The disadvantages and inadequacies of these prior art passageway formingmethods have become increasingly serious as modern casting operationshave become more complicated entailing the increased use of many smallbore passageways of complex shapes. While there are some refractorymaterials such as glass, quartz, carbon and plaster which are availablefor molding into cores capable of producing intricately formedpassageways, the use of these materials has been found limited inapplication due to the difficulties accompanying the molding of thematerials into the desired shape, the formation of scrap castings due tothe use of non-permeable core materials, as well as the difficultiesaccompanying the removal of the cores from the formed casting.

It is an object of the present invention to overcome the aforementioneddifiiculties as well as generally improve the art of forming coredpassageways in metal castings by the provision and use of a new type ofcore element which may be readily formed in many desirable shapes andsizes, which is inexpensive to form, which is capable of supplying tothe finished casting an accurately placed cored passageway, which iscapable of efliciently venting any gas that may be generated on thesurface of the core, and which may be readily removed from the castingto thereby produce a casting that is radiographically andmetallurgically sound in the area surrounding the cored passageway.

Another object is to provide a method of forming castings having coredpassageways therein, which method makes use of the improved core elementto thereby substantially simplify casting procedures.

Certain other objects of the invention will in part be obvious and inpart appear hereinafter.

It is intended by the present invention to make use of a core element infoundry castings which includes a flexible gas-permeable refractorysleeve. Preferably the sleeve is formed from braided, woven or suitablymatted glass fibers or asbestos but it is intended to include within thescope of the present invention the use of any flexible refractorymaterial which is capable of being braided, woven or matted in such amanner as to 'form a gaspermeable sleeve. Such sleeves are normallycollapsible and therefore must be made sufficient-ly rigid to be capableof retaining their shape while positioned in the mold during the castingoperation. There are several different procedures available which arecapable of supplying the sleeve with the requisite rigidity. One of suchprocedures includes the interweaving of thin metallic strips or threadswith the glass fiber in the formation of the sleeve to provide thesleeve with increased rigidity while at the same time retaining therequisite permeability and flexibility of the sleeve. This procedure isparticularly adapted for use in the formation of sleeves having smalloutside diameters such as on the order of inch to M inch or even less.

from a metal having a melting point lower than that of the metal of thecasting. Under these circumstances the casting is cooled sufficiently-tosolidify the cast metal immediately outside and in contact with therefractory, permeabl'e sleeve while the 'over-all'temperature ismaintained at a degree sufficient to retain the core supporting wire ina molten state. The wirestrand may then be poured from the passageway ofthe casting followed by subsequent manual removal of the sleeve.

A preferred procedure of internally supporting the sleeve sufiicientlyto impart adequate rigidity to the sleeve to withstand the weight ofthemetal being cast includes the use of tubes formed from a metal which issoluble in solvents which do not attack the metal of the casting. Thesemetal tubes are available in a wide range of sizes and, as a result, arecapable of a wide variety of applications. Obviously, tubes of a'widerange of diameters and various cross sectional configurations may beused according to this invention 'In the use of joined segments oftubing as an internal support of a flexible refractorysleeve of the typedescribed, it is unnecessary that the tube segments be perfectly joinedas'the continuous outer surface of the flexible sleeve insurestheformation of a smooth passageway as well as accurate joints. Aspreviously described, the exacting skill normally required in theformation of cast-in tubes 'is not necessary as the flexible sleeve is,capable of counterbalancing imperfections at the joints of thesupporting tube. All that is required of a supporting tube is that it becapable of imparting to the sleeve the requisite rigidity necessary towithstand casting conditions while presenting a sufliciently accurateexterior to prevent raised or depressed points in the sleeve. Thesupporting tubeis inserted within a finished'sleeve or the sleevematerial,'such as glass fiber strands, may be actually braided over thetube to thereby form a much smoother surface resulting in a'smoothercoredhole in thec'astiug.

Ductile tubing, such as certain grades of copper and softsteeltubing,may be used in a continuous form under circumstancesnormally making its use undesirable. For example, if a bare copper tubeis cast in aluminum, a scrap casting will result as the aluminum willdissolve the copper until all of the latter is used up. Due to'thepresence of the sleeve the use of ductile copper tubing is greatlyexpanded. Obviously, duc'tile'tubing is a preferred source of tubing asit can be readily pre-shaped to conform with the shape of passagewaydesired. The copper, due to the presence of the sleeve which acts as abarrier, is prevented from being dissolved by themetal of the casting.

An important advantage of utilizing a tube as an internal support 'ofthe sleeve is to provide an internal passageway within the core elementfor the introduction of a solvent capable of dissolving the metallictubing while at the same time being ineifective with respect to themetal of the casting. Following the removal of the dissolved metaltubing from within the sleeve, the latter may be manually withdrawn fromthe passageway of the casting.

A further advantage residing in the use of a hollow metallic tube isthat the tube may be perforated, as by drilling, at regular intervalsfor the purpose of helping to remove any gas formed on the surface ofthe glass fiber sleeve when the molten metal is' poured. Due to thepermeability of the sleeve the gas can escape through the sleeveand thedrilled holes into the tube and through the tube out of the casting.

The general method of forming cored passageways will now be morecompletely described in connection with the drawings, wherein:

FIG. 1 is a perspective view of a wooden form with a length of ductilemetallic tubing formed in position thereon;

FIG. 2 is a perspective view of the core element including the outergas-permeable refractory sleeve positioned about the internallysupporting metallic tube, which core element is ready for placement in amold;

FIG. 3 is an enlarged cross section of the core element of FIG. 2;

FIG. 4 is a perspective view of the completed mold illustrating theposition of the core element of FIG. Zin

the mold as indicated by the dotted lines;

FIG. 5 is an enlarged fragmentary perspective view of a manner in whichthe metallic tubing may be removed from the sleeve within the finishedcasting;

FIG. 6 is an enlarged fragmentary cross-sectional view of the castingillustrating the partial removal of the metallic tube from the core;

FIG. 7 is a view similar to FIG. 6 illustrating the total removal of themetallic tube from the core;

FIG. 8 is an enlarged perspective view of the casting illustrating theremoval of the sleeve from the cored passageway of the casting;

FIG. 9 is an enlarged partial cross-sectional view of the'coredpassageway in the casting following removal of the core element; and

FIG. 10 is a graph setting forth a curve representing the solubility ofmagnesium in mixtures of nitric and hydrofluoric acids.

Referring to FIG. 1, a wooden form 10 is shown as containing a-number ofcurvilinear sections, such as 11 and 12, which cooperate to serve as apattern for the preshaping of the core element. To provide the castingwith a small diameter multi-curved internal passageway, it'has beenfound desirable to utilize a core element 13 as shown in FIGS. 2 and 3.The particular core element 13 illustrated is formed from an outerflexible gas-permeable sleeve "14 of woven glass fibersinternallysupported by a copper tube 15. Certain grades of coppertubing, being ductile, may be bent to conform with the shape of thepassageway desired in the casting. An-example of this procedure isillustrated in FIG. 1 wherein the copper tube 15 is shown as positionedon the wooden form 10 and pre-shaped to its contour.

Following the pre-shaping of the copper tubing 15 the glass fiber sleeve14 is positioned about the tubing and the core element is ready forinsertion within the mold. FIG. 4 illustrates a known manner ofobtaining a metal casting of intricate shape. A pattern is used in theconventional manner to form the mold cavity ingreen or dry sand or othersiliceous materials. The core element 13 is positioned within a cope 16and drag 17 as illus trated by the dotted lines. The mold is providedwith a gate 18 and sprue passageways 19 through which the molten metalis introduced into the mold. The cope16 further includes a riser 20which provides for a reservoir of metal to counteract shrinkage of thecasting in the known manner. The ends of the core element 13 asdesignated by the numeral 21 extend outwardly of the mold cavity intocore prints in the sand. In this manner the core 13 is supported by itsends 21 in a suspended manner within the mold cavity to properlyposition the passageway to be formed in the casting. Gas trapped aboutthe core element 13 by the incoming molten metal is allowed to permeatethrough the sleeve 14 and ultimately escape out of the mold cavity. Thisfeature is of particular importance in the present invention as withoutthe Provision of means for allowing the trapped gas to escape-from themold cavity, gas pockets would be formed in the casting about theinternal passagewaytherein and the casting would be imperfect probablyto the extent that itwould be completely non-useable.

'In FIG. 5 a finished castingZZ is shown as still coutaining the coreelement 13 within the internal passageway formed thereby. The first stepin removing the core element 13 from the passageway involves theconnection of an inlet or solvent line 23 to one end of the passagewayof the casting 22 and an outlet line 24 to the other end of thepasageway of the casting 22. The outlet line 24 may be connected to asource of vacuum if necessary or a stainless steel lined centrifugalpump may be used and a solvent which is capable of dissolving the coppertube 15 while at the same time being ineffective or passive with respectto the metal of the casting 22 is introduced into the line 23 and flowsthrough the interior of the copper tube 15 throughout the entire lengthof the core element 13. An example of a solvent suitable for use indissolving copper tubing from a core element used in a magnesium castingis 33% nitric acid combined with 67% hydrofluoric acid. This mixture ofacids is capable of efficiently removing the copper and the glass fibersleeve from the casting without aflecting the magnesium of the casting.In the instance where the casting is formed from aluminum, it has beenfound that nitric acid alone may be used to remove the copper withoutdestroying the sleeve. In line with the last mentioned circumstances,FIG. 6 illustrates partial solvent removal of the tube 15 indicating itsinitial inside diameter by the dotted line 25. Ultimately, only thesleeve 14 remains within the passageway of the casting 22 as illustratedin FIG. 7. The sleeve 14 is then manually withdrawn from the casting 22,as illustrated in FIG. 8, and the desired intricate passageway 26remains within the casting 22.

FIG. 9 illustrates the type of passageway 26 formed as a result of theabove described operations and it can be seen that the pasageway 26 issubstantially smooth and perfectly formed, By following this procedure,the passageway 26, even though intricate throughout its length, is, incross section, uniform in shape and dimensions. It is unnecessary toresort to subsequent machining operations to insure the obtaining of apassageway consistent with respect to a desired diameter throughout theentire length thereof. Furthermore, due to the refractory and permeablenature of the sleeve 14, gas trapped within the mold by the castingoperation is allowed to escape from the passageway and no undesirablegas pockets are present to deform the passageway during the formationthereof. Obviously, the tube 15 may be of any desired crosssectionalshape to form square, rectangular, oblate, elliptical, etc. passageways.The tube may vary in its crosssectional shape throughout its length. Thesleeve 14 is adapted to conform to the shape of the tube 15 and willnormally increase the outer diameter of the tube 15 approximately 0.02of an inch.

It will be seen that the core element 14 is inexpensively and simplyformed. There are no disadvantages present resulting from havingimperfect interiors in the passageway of the casting due to imperfectjoints existing in the core element, weld spatter or flowing weldmaterial. Glass fiber has the ability to allow the molten metal to lieagainst it in such a manner as to result in the formation of asubstantially smooth interior in the passageway. The surface of the casthole may be made smoother by rubbing the surface of the sleeve 14 with afiller such as a dry plumbago or titanium dioxide. This will fill in theinterstices of the refractory material and aid in the formation of asmoother wall. The sleevei easily removed manually from the passageway,as demonstrated in FIG. 8, regardless of the complexity of thepassageway because of its strength, flexibility and pliability.Efficient and intact sleeve withdrawal is obtained by reason of thedirecting of the sleeve in the mold for full circumferential outersurface contact with the casting metal and for coinciding longitudinalcenter line positioning in the passageway formed thereby in the casting.

In the instance where a ductile copper tube is utilized in internallysupporting the core element, the glass fiber sleeve guards against amixing of the copper in the molten metal of the casting such as wouldoccur in the instance where an unprotected coppercore is used in analuminum alloy casting, In preventing mixing of the copper, the coppertube may be completely removed from the casting and the metalsurrounding the passageway formed in the casting does not have itsproperties changed as a result of an increase in copper concentration.From this it can be readily seen that by reason of the "sleeve, coppertubing can be put to a wide variety of uses in the casting art. Thislatter feature is of importance due to the desirable property ofductility existing in certain grades of copper.

While the foregoing explanation made in conjunction with FIGS. 1-9 hasdealt primarily with the use of a sleeve formed from glass fibers andinternally supported by ductile copper tubing, it should be understoodthat it is well within the scope of the present invention to make use ofother suitable materials capable of bringing about the advantagespreviously discussed. The basic concept of the present invention is tomake use-of material'which is capable of being braided or woven to forma flexible gas-permeable refractory sleeve for use in the same manner asdescribed in connection with the glass fiber sleeve. In the event thatmetallic material is utilized in forming such a sleeve any strips orwires of a metal not soluble in the molten metal of the casting or inthe particular acid used to remove the internal supporting tubingtherefrom may be used. By referring to the materialas being refractorymaterial, it is meant that such material is capable of withstanding thetemperatures used in the casting operation without being affectedthereby.

As a further illustration of the type of material highly adaptable foruse in the forming of a flexible gas-permeable sleeve, it'has been foundthat braided or woven wire strands of stainless steel produce a sleeveparticularly adapted for use in the formation of a passageway in amagnesium alloy casting. The diameter of the Wires used in forming astainless steel sleeve will normally fall within the area of 0.0036 ofan inch. Stainless steel is not soluble in molten magnesium and, as aresult, a casting having a variance in metallic composition in thevicinity of its cored passageway will not result from the use of astainless steel sleeve.

Still referring to the use of a stainless steel sleeve-in the formationof a cored passageway in a magnesium alloy casting, additionaladvantages are present. For example, once the casting has been formedand it is desired to remove the tubing internally supporting the sleeveprior to the removal of the sleeve, the acid used would preferably be asuitable mixture of nitric and hydrofluoric acids. The hydrofluoric acidis present in the mixture to passivate the mixture with respect to themagnesium alloy so that the latter will not be damaged by acid action.The acid mixture, being passive with respect to the magnesium castingand the sleeve, will dissolve the sleeve-supporting tubing, such ascopper tubing, following which the unaffected sleeve may be manuallyremoved and a clean bore is left in the casting.

It is generally considered desirable to make use of a material informing the sleeve which will not be afiected by the acid or acidmixtures used in removing the sup porting tubing. In the casting ofmagnesium, it is essential that the nitric acid used in removing thecopper tubing be passivated by the presence of suflicient amounts ofhydrofluoric acid thereby alleviating acid action with respect to themagnesium of the casting. When a glass fiber sleeve is used under thesecircumstances, the hydrofluoric acid present in the mixture attacks theglass fibers and the sleeve is at least partially destroyed to an extentthat its continuity is interrupted and its strength is materiallyreduced thereby eliminating the possibility of manually withdrawing thesleeve from the cored passageway of the casting. While a substantiallyclear bore may still be obtained it is nevertheless necessary to resortto other techniques in removing the damaged glass fiber sleeve from thecored passageway. Such techniques, for example, include the use of airblasts or wet sand blasting which, of course, involves the cost ofmaking available additional equipment for use in the foundry.

Toovercome this last mentioned problem, the sleeve maybe-formed from amaterial'which is capable of withstanding hydrofluoric acid action andretaining its continuity and strength. Such material, under the specificconditions set forth above, is stainless steel and a sleeve of wovenstainless steel wires will perform in the manner desired during thecasting operation and in addition be unaffected by the action of thehydrofluoric acid contained in the acid mixture. As a result, thestainless steel sleeve may be manuallywithdrawn fiom the coredpassageway without the necessity of using air blasts or otherspecialized procedures. Since the stainless steel sleeving is betweenthe ductile iron or copper tube and the cast metal, the manual removalof the sleeve is excellent evidence of the cleanliness of the coredpassageway.

In FIG. 10 a graph is presented which illustrates the variation insolubility of a magnesium alloy in a mixture of nitric and hydrofluoricacids, which mixture varies with respect to the hydrofluoric content.The curve presented in FIG. 10 was derived from determining the percentweight loss of magnesium with varying percentages of hydrofluoric acidin the mixture of acids. An immersion time of 1 hour was used in eachinstance and the alloy tested was typical of available magnesium alloys,all of which have a magnesium content of at least 90%, the particularalloy tested having the following composition:

The nitric acid commercial-source used was a 70% grade while thehydrofluoric acidwas a 50% grade. The curve presented in FIG. 10' is asemi-logarithmic curve, the ordinate representing the percent loss ofmagnesium being plotted on a logarithm scale and the abscissarepresenting the concentration of hydrofluoric acid being plotted on anarithmetic scale.

In considering the curve presented in FIG. 10, it will be noted that asthe percent concentration of hydrofluoric acid increases in the mixture,the percent loss of magnesium decreases. In foundry operation it is ofcourse desirable to maintain the loss of magnesium at a minimum while atthe same time maintain the concentration of nitric acid in the acidmixture at a level sufficient to properly dissolve the supporting tubeof the core element. A mixture of equal quantities by volume of theseacids has been'found adequate for use in foundry production and inreferring to the graph of FIG. 10 it will be noted that under suchcircumstances the percent weight loss of magnesium will be maintained atwell below 0.1%. At the same time it has been found that 50% nitric acidis capable of dissolving the supporting tube of the core element withina reasonable time.

Whereas the element copper is soluble in molten magnesium alloys, asleeve composed of sutficiently fine and closely woven stainless steelwires placed about the copper tube prevents the solution of the latterin the mag nesium alloy. While copper has been referred to almostexclusively because of the ductile nature of certain grades of copper,it should be understood that any suitable supporting tubing capable ofcarrying out the principles of the present invention may be used. Forexample, tubing formed from soft steel exhibits ductile properties whichallow such tubing to be readily used in forming intricate passageways incastings ofthe type above discussed. Soft steelof the type designated asSAE 1015 has been found to be highly adaptable for use. The soft steelwill be dissolved by the nitric acid of the acid mixture and will not beaffected by thewmolteumagnesium inthe. event that contact should be madetherebetween. -It should :be further understood that the .glass fibersmaybe iinterwoven with steel wires to form a sleeve for use in amagnesium-casting. Due to the presence of hydrofluoric acid-in the acidmixture someof the glass'fibers may -be dissolved thereby; however, thepresence of the-steelwires being unaffected by the hydrofluoricacid willprovide the sleeve with adequate strength and continuity to allowsubsequent-manual withdrawal of the-sleeve from the cored passageway inthe casting.

The following examples are illustrative-of-metho'ds of forming coredpassageways in castings which incorporate the principles of the presentinvention. However, it should be understood that these examples, beingillustrative, are notintended to be construed as limiting the scope ofthe present invention.

Example I A Wooden form was constructed to conform with a desired shapeof a metal casting to which was to be supplied an intricate internalpassageway. A soft copper tube of inch outside diameter was pre-shapedby pressing the latter against the wooden form to conform with thedesired intricate longitudinally extending shape of the contemplatedpassageway. The pre-formcd copper tube was then sheaved'with a sleeve ofwoven glass fiber of the type sometimes used as wire insulation onelectric motors. The assembled core element was then placed in apro-shaped cavity of a sand mold and molten aluminum alloy, No. 355 ofthe Aluminum Company of America, was poured into the mold cavity at atemperature of 1380 F. The mold was allowed to cool and the casting wasshaken out after which the heads, risers and gates were removedfollowing normal foundry cleaning room methods. The casting passagewaywas further enlarged at its extremities with a drill of /2 inch diameterto an extent of approximately /2 inch in depth. Into these enlargedholes rubber tubing was placed. One tube was attached to a glass funneland the other tube to a water aspirator with a suitable overflow bottle.1500 cc. of concentrated nitricacid was passed through the coredpassageway. This acid dissolved the copper tube, and the solution wasdrawn into the water aspirator. The pasageway was then washed throughwith water following which approximately 25 cc. of fresh, copper free,nitric acid was passed through the passageway and tested for coppercontent with sodium sulfide. The test was negative indicating that allcopper had been removed from the core element. The passageway was againwashed with water and 300 cc. of carbon tetrachloride was passedtherethrough. The casting was disconnected from the washing arrangementand the passageway blown dry with compressed air. The latter actionpartially pushed the glass fiber sleeve out of the small coredpassageway whereupon it was easily fully removed by pulling. The glassfiber sleeve was intact despite the previous operations perforrned'incasting the metal and removing the inner copper core.

Example II A wooden form was constructed to conform with a desired shapeof a metal casting to which was to be supplied an intricate internalpassageway. A ductile soft steel tube formed from SAE 1015 steel ofapproximately & inch outside diameter was pro-shaped by pressing itagainst the wooden form to conform with-the desired intricatelongitudinally extending shape of the contemplated passageway. Thepro-formed steel tube was then sheaved with a sleeve of woven stainlesssteel wires, each having a diameter .of approximately 0.0036 of :aninch. The assembled .core element was then placedinia .pre shaped cavityof a sand mold and molten magnesium alloy identified as ZRE 1 suppliedby Magnesium Elek- 9 tron Limited of London, England, and having ageneral composition as follows:

The stainless steel used in forming the sleeve had an approximatecomposition as follows:

percent Chrome 18 Nickel 8 Maximum carbon .05 Iron Remainder The moltenmagnesium alloy was poured into the mold cavity at a temperature ofaround 1400" F. The mold was allowed to cool and the casting was shakenout after which the heads, risers and gates were removed followingnormal foundry cleaning room methods. The casting passageway was furtherenlarged at its extremities with a drill of /2 inch diameter to anextent of approximately 12 inch in depth. Into these enlarged holesplastic tubing was placed. One tube was attached to a plastic funnel andthe other tube to a polyethylene bucket. One gallon of a mixture of 5 0%by volume of 70% grade hydrofluoric acid and 50% by volume of 38 Baum(69- 71% grade) nitric acid was passed through the cored passageway.This acid mixture dissolved the steel tube and the resulting solutionwas drawn into the bucket. The passageway was then washed through withwater and dried following which the stainless steel sleeve was manuallywithdrawn therefrom. It was found that the sleeve was intact and wasreadily and completely removed from the cored passageway.

The copper tube used in the aluminum casting is interchangeable with asoft steel tube. The stainless steel sleeve may be used with eitheraluminum or magnesium alloys. A glass fiber sleeve is preferred for usewith aluminum while a stainless steel sleeve is preferred for use withmagnesium alloys to eliminate partial destruction by the action ofhydrofluoric-nitric acid mixtures.

While certain acid solvents have been specifically referred to, itshould be understood that any suitable solvent may be used in carryingout the method of the present invention. The solvents used will dependupon the type of material forming the sleeve and the supporting tube. Afurther consideration in determimng the proper solvent for use residesin the type of metal used in the casting. The principal function of thesolvent is to remove the supporting tube from the core element and indoing so this solvent should preferably be ineffective against the metalof the casting.

If desired, m'pples surrounding a portion of the core ends 21 may beformed integral with the ends of the castings. In this manner flexible,acid resistant tubing, such as rubber or Tygon, which is a compoundedhalide polymer, condensation resin and diene derivative, made by US.Stoneware C0., of Akron, Ohio, may be suitably attached to the nippleswithout the necessity of widening the ends of the passageway.

In order to obtain the best results in the shortest time it has beenfound that the dissolving of the sleeve-supporting tubing shouldpreferably be carried out at a temperature within the range of 70 to 140F. Within this range the acid apparently is most effective and thedissolving action is obtained in the shortest possible time. It shouldbe understood, however, that this range is considered merely to bepreferable and should not be construed as a limiting factor in carryingout the various procedures of the present invention.

While specific reference has been made to the formation of curvedpassageways of an intricate nature, it should be understood that thecore element including the sleeve and supporting tubing may be readilyused inforniing straight line bores in castings. The core element of thepresent invention, of course, eliminates the many difficultiesaccompanying the formation of curvilinear passageways in castings.However, the core element is also very useful in the formation ofstraight line passageways. When the core element is used in the lattersituation it is possible to manually remove the supporting tube fromwithin the sleeve following which the sleeve will collapse inwardly andmay be readily removed manually from the bore. It is generallyconsidered in ,conventional foundry practices that in the forming ofstraight bores in castings, a tube of a length of no greater than fivetimes its diameter may be used without a resultant scoring of the innersurface of the passageway caused by the removal of tubes of a greaterlength. By making use of a sleeve element the supporting tube may be ofany length desired as it will not come into contact with the surface ofthe casting defining the bore. In this connection, tubes of A; inchdiameter and 20 inches long have been successfully used without scoring.

This application is a continuation-in-part of my copending application,Serial No. 538,091, filed October 3, 1955, now abandoned.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. A passageway forming core element for use in making foundry castings,said element including a flexible gas-permeable refractory wovenstainless steel sleeve internally supported by copper tubing which issoluble in solvents ineffective with respect to the metal of saidcastrugs.

2. The method of forming a cored passageway of substantially controlleddimensions in a metallic casting which comprises: inserting within amold a flexible gas-permeable sleeve formed from woven strands ofrefractory material and internally supported by metallic tubing, pouringsaid mold, dissolving said tubing with a solvent ineffective withrespect to the material of said sleeve and the metal of said casting,and thereafter manually withdrawing said sleeve from said casting.

3. The method of forming a cored passageway of substantially controlleddimensions in a metallic casting which comprises: inserting within amold a flexible gaspermeable sleeve formed from woven strands ofrefractory material and internally supported by a metallic memher havinga melting point less than the metal of said casting, pouring said moldto surround said sleeve with molten metal, cooling said metal to atemperature above the melting point of said member, flowing the moltenmetal of said member out of the interior of said sleeve, and thereaftermanually withdrawing said sleeve from said casting.

4. The method of forming a cored passageway of substantially controlleddimensions in a magnesium casting which comprises: inserting within amold a flexible gaspermeable sleeve of woven stainless steel strandsinternally supported by soft steel tubing, pouring said mold to surroundsaid sleeve with molten magnesium, cooling said magnesium, dissolvingsaid tubing with an acid mixture of approximately 50% nitric and 50%hydrofluoric, and thereafter manually withdrawing said sleeve from saidcasting.

5. The method of forming a cored passageway of substantially controlleddimensions in an aluminum casting which comprises: inserting within amold a flexible gaspermeable sleeve of Woven glass fibers internallysupported by copper tubing, pouring said mold to surround said sleevewith molten aluminum, cooling said aluminum, dissolving said tubing withnitric acid, and thereafter manually withdrawing said sleeve from saidcasting.

"a ac 52b 6. The method of forming -a cored-passageway'of' substantiallycontrolled dimensions in a metallic casting which comprises:inserting-within a mold -a gas permeable sleeve of inter-twinedstainlesssteel strands internally supported by copper tubing, pouring said moldto surround said sleeve with molten metal, cooling said metal,dissolving said tubing with a mixture of nitric acid and hydrofluoricacid which is passive-with respect to' the metal of said casting andthereafter -manually withdrawing said'sleeve from' said casting.

'7. A mold foruse in the formation of a metallic casting, said moldincluding a-mold cavity 'provided with means for receiving metallicmaterial thereinto, and a'core element supported in said cavity to'besurrounded by metallic material, said core element consisting of aflexible andgas-permeable, sleeve formed'from woven-strands ofrefractory material, and reinforcing means received in said sleeve tosupport the same against radial collapse, said sleeve being directed insaid .mold for full circumferential outer surface contact with saidmetallic material and for coinciding longitudinal center linepositioning in a passageway formed thereby in a casting to permit intactmanual withdrawal thereof'from said passageway.

8. The method of forming a cored passageway of substantially controlleddimensions-in a metallic casing which comprises: inserting within a molda flexible gas-permeable sleeve internally supported by a metallicmember, said sleeve being formed from woven strands of refractorymaterial, pouring said mold, removing said metallic member from theinterior of said sleeve, and thereafter manually withdrawing said sleevefromsaid casting.

9. A passageway forming core element for use in making foundry castings,said element including a flexible gas-permeable sleeve formedfrom wovenstrands of 12 refractory material, said sleeve being internallysupported by a metallic member.

10. A passageway forming core element for nsedn making foundry castings,said element including a flexgas-permeable sleeve formed from wovenstrands of ,re-

fractory asbestos, said sleeve being internally supported by ametallic'member.

References Cited in the. fileof thislpatent UNITED STATES PATENTS 8,570Warner Dec. 2, 1851 818,413 Caldwell Apr. 24, 1906 1,310,768 Nugent July22, 1919 1,416,412 Pack May 16, 1922 2,045,556 Almen June 23, 19362,173,955 Zahn Sept. 26, 1939 2,304,879 Brazil Dec. 15, 1'942 2,362,8757 Zahn Nov. 14, 1944 2,373,405 Lowit Apr. 10, 1945 2,489,280 Flora'et alNov. 29', 1949 2,688,781 Fahlberg et a1 Sept. 14, 1954 FOREIGN PATENTS575,734 Great Britain Mar. 4,1946

